1. Properties of Water Chapter 2 Section 2

2. Objectives  Discuss the unique properties of water  Differentiate between solutions and suspensions  Explain what acidic solutions and basic solutions are

3. The Water Molecule  Its properties and functions stem from its chemical structure  It is one of the few compounds found in a liquid state over the Earth’s surface  It is a neutral molecule  Is essential for all biological processes

4. Structure of Water  Made of 2 hydrogen atoms covalently bonded to 1 oxygen atom

5. Polarity  The electrons are not shared equally between the oxygen atom and the hydrogen atoms  This unequal sharing causes partial charges to occur at opposite ends of the molecule  A molecule in which the charges are unevenly distributed is called polar  The polarity of water molecules also gives it a bent shape

6. Hydrogen Bonding  Because of polarity, water molecules are attracted to each other  They form hydrogen bonds between the partial positive charge of the hydrogen atoms of one molecule to the partial negative charge of oxygen on another molecule  Hydrogen bonds are the force of attractions between hydrogen molecules and other atoms such as oxygen, nitrogen & fluorine  These bonds form, break, and reform with great frequency  Polarity of water and hydrogen bonding are responsible for the other properties of water

7. Properties of Water  Cohesion  Adhesion  Heat Capacity  Solvent nature

8. Cohesion  Cohesion is an attraction between molecules of the same substance  Water molecules can be involved in as many as 4 hydrogen bonds at the same time, making it extremely cohesive  Cohesion causes water molecules to be drawn together, which is why drops of water forms beads on a smooth surface  It is also responsible for surface tension which makes water acts as if it has a thin “skin” on its surface  Surface tension also enables small creatures such as spiders and water-striders to run on water without breaking the surface

9. Adhesion  Adhesion is the attractive force between molecules of different substances  For example: water molecules and glass molecules  The surface of water becomes curved because the attraction between the water and glass molecules is greater than the cohesion between water molecules  Adhesion between water and glass molecules also cause water to rise in a narrow tube against the force of gravity  This affect is called capillary action  Plants use capillary action to draw water from its roots to its leaves

10. Cohesion and Adhesion in Action  Trip to ISS Trip to ISS  Mini Lab!  How many drops of water can you get on a penny before it spills over?

11. Heat Capacity  Due to multiple hydrogen bonds between water molecule, it takes a large amount of heat energy to speed those molecules up and create a rise in temperature  Water’s heat capacity, the amount of heat energy required to increase temperature, is relatively high  This allows:  Bodies of water to absorb large amounts of heat with only small changes in temperature  Cells to regulate temperature  Stabilizing of global temperatures  Evaporative cooling

12. Water Mixtures  Water is not always pure  It is often part of a mixture  A mixture is a material composed of two or more elements that are physically combined and not chemically combined  For example:  Salt & pepper  Sugar & sand  Air  Living things are mixtures involving water  Two types of mixtures with water:  Solutions  Suspensions

13. Solutions  A solution is a mixture in which 1 or more substances are uniformly distributed in another substance  They can be mixtures of liquids, solids, or gases  For example: Blood Plasma  They are made up of two components: the solute & the solvent  Water’s polar nature allows it to dissolve polar substances  Examples: sugar, ionic compounds, some proteins

14. Solute vs. Solvent  Is a substance dissolved in the solvent  Can be ions, atoms, or molecules that are dispersed  Is the substance that does the dissolving  Example: water (universal) In a solution of sugar water, sugar is the ___________ and water is the ____________.

15. Solutions Continued  Solutions can have varying concentrations  which is the amount of solute in a certain amount of solvent  Example: 5% saltwater solution is 5g of salt dissolved into 100 mL of water  Saturated solution: is one in which no more solute can dissolve  Aqueous solution: is one in which water is the only solvent

16. Suspensions  Some materials do not dissolve when placed in water, but separate into pieces so small that they do not settle out  The movement of the water molecules keeps the small particles suspend  Mixtures of water and undissolved material are called suspensions  Some of the most important biological fluids are both solutions and suspensions  For example: blood

17. Blood as a Solution & Suspension

18. Ionization of Water  Occurs when water molecules are pulled apart or dissociate into ions  When this happens it leaves hydrogen to bond with another water molecule forming the hydronium ion Hydroxide ion Hydrogen ion

19. pH  Chemists devised a measuring system called the pH scale to indicate the concentration of H+ ions in solution  The pH scale ranges from 0 to 14  Each step on the pH scale represents a factor of 10

20. pH Determinations  The pH of a solution is determined by the amount of hydrogen ions or hydroxide ions present  At a pH of 7, the concentration of the H+ ions and OH- ions is equal so its called neutral  Solutions with a pH below 7 are called acidic because they have more H + ions than OH - ions  Solutions with a pH above 7 are called basic because they have more OH - ions than H + ions

21. Acids & Bases Acids  Is any compound that forms H + ions in solution  Strong acid pH values range from 1 to 3  Tend to have a sour taste  Can be corrosive  For example  HCl  H 2 SO 4 Bases  Is any compound that forms OH - ions in solution  Strong base pH values range from 11 to 14  Tend to have a bitter taste  Tend to feel slippery  For example:  NaOH  NaHCO 3

22. Buffers  The pH of the fluids within most cells in the human body must generally be kept between 6.5 and 7.5  If the pH is higher or lower it affects the chemical reactions within the cells  Controlling pH is a matter of homeostasis and is done using buffers  Buffers are weak acids or bases that can react with strong acids or bases to prevent sudden changes in pH  For example: bicarbonate and phosphate ions